"The distances that need to be covered are huge," Rear Admiral Vasileios Gryparis told AFP at EU operation headquarters in the central Greek city of Larissa.

"So far, because shipping is down by over 50 percent, it is possible to escort any ship that requests protection."

"We have accompanied 79 ships so far and none has sustained damage whilst under our escort."

"This is a point of reference on which we can build to increase the number of ships under protection... with the means currently at our disposal, this is not possible," he said.

Operation Aspides, named after the Greek word for shield, was launched by the European Union in February with the goal of protecting international shipping.

The Huthis began attacking ships in the Gulf of Aden and the Red Sea in November, a campaign they say is intended to signal solidarity with Palestinians in Gaza.

They have vowed to target Israeli, British and American ships, as well as vessels heading to Israeli ports, disrupting traffic through the vital trade route off Yemen's coasts.

In March, the US defence department said Huthi rebels had attacked civilian and military ships sailing off Yemen's shores at least 50 times since their assaults began.

The attacks have sent insurance costs spiraling for vessels transiting the Red Sea and prompted many shipping firms to take the far longer passage around the southern tip of Africa instead.